Quarterly report pursuant to Section 13 or 15(d)

Derivative Instruments and Hedging Activities (Schedule of Derivative Instruments in Statement of Financial Position, Fair Value) (Details)

v3.8.0.1
Derivative Instruments and Hedging Activities (Schedule of Derivative Instruments in Statement of Financial Position, Fair Value) (Details) - Not Designated as Hedging Instrument - USD ($)
$ in Thousands
Sep. 30, 2017
Dec. 31, 2016
Offsetting Assets and Liabilities [Line Items]    
Derivative asset $ 4,454 $ 103
Derivative liability 7,039 18,296
Current assets: Fair value of derivatives    
Offsetting Assets and Liabilities [Line Items]    
Derivative asset, fair value, gross asset 5,441 1,836
Derivative asset, fair value, gross liability (2,108) (1,733)
Derivative asset 3,333 103
Long-term assets: Fair value of derivatives    
Offsetting Assets and Liabilities [Line Items]    
Derivative asset, fair value, gross asset 1,388  
Derivative asset, fair value, gross liability (267)  
Derivative asset 1,121  
Current liabilities: Fair value of derivatives    
Offsetting Assets and Liabilities [Line Items]    
Derivative liability, fair value, gross liability (8,488) (20,001)
Derivative liability, fair value, gross asset 2,108 1,733
Derivative liability 6,380 18,268
Long-term liabilities: Fair value of derivatives    
Offsetting Assets and Liabilities [Line Items]    
Derivative liability, fair value, gross liability (926) (28)
Derivative liability, fair value, gross asset 267 0
Derivative liability $ 659 $ 28